But XQuery (and XPath, being its subset) is pretty much just pure sequence comprehensions for the XML Data Model. It might have been unusual from a mainstream PL perspective back when it was introduced, but today, when C# has LINQ, and JS developers preach the miracles of map/filter/fold over immutable data structures, I don't think XQuery is all that exotic.

JSON has no querying system, it can only be accessed by deserializing to an in-memory object or using whatever custom APIs are available (like postgres json functions).

JsonPath is the proposed standard, and it looks pretty much like XPath. And that's before getting into Json Schema.